The present invention relates to procedures for the detection or for the determination of solid phase-associated factors, which are multiply associated with the same solid phase. According to the invention, the sample is brought into contact with a transmitter particle, on which at least one ligand having binding affinity for a solid phase-associated factor and a transmitter are immobilized, and a receiver particle, on which at least one ligand having binding affinity for said solid phase-associated factor and a receiver is immobilized, and then the signal is determined which results when transmitter and receiver are brought sufficiently close to one another. In particular, the invention relates to the detection of cell surface receptors which can be used for the typing of cells or for the determination of cell activation states. It is thus possible to replace the hitherto widely customary flow cytometry by a more simple procedure.
The differentiation of blood cells, in particular of leucocytes granulocytes, monocytes and lymphocytes) is a routinely used and important procedure in diagnostics. It is based, inter alia, on the fact that different cell types are characterized by different surface antigens, such as, for example, membrane proteins of the integrins family (Hynes R O. Integrins: a family of cell surface receptors. Cell 1987; 48: 549-554) (incorporated herein by reference). Most of these membrane proteins are designated by CD numbers (cluster designation numbers).
Membrane proteins can also only be exposed on the surface after stimulation of the cells or secreted by fusion of intracellular vesicles with the surface, such as, for example, proteins from the selectins group (Bevilacqua M P and Nelson R M. Endothelial-Leukocyte adhesion molecules in inflammation and metastasis. Thromb. Haemost. 1993; 70: 152-154) (incorporated herein by reference).
In the case of platelets, for example, GMP-140 (P selectin; DC62P) is an activation marker. Furthermore, in activation states characteristic complexes of receptors of cells and ligands can result, such as, for example, on activated platelet complexes of the glycoproteins GP Ib/IX or GP IIb/IIIa, which bind von Willebrand factor or fibrinogen (see, for example, Clemetson K J. Biochemistry of platelet membrane glycoproteins, Prog. Clin. Biol. Res. 1988; 283:33-75) (incorporated herein by reference). After activation, phosphatidylserine-containing lipid membranes, to which clotting factors or other phospholipid-binding protein (for example from the annexins family) can bind, are also exposed on platelets.
In previous procedures, labeled antibodies or other labeled reactive ligands, for example annexins, against these surface antigens were added to blood for the detection of phosphatidylserine-containing lipid membranes (Rxc3x6misch J et al., Anticoagulant properties of placenta protein 4 (annexin V); Thromb. Res. 1990; 60: 355-366) (incorporated herein by reference). By means of flow cytometry, the cells are then sorted according to their size and in the course of this a conclusion is drawn at the same time via the detection of the labeling on the number and proportions of one or several cell types in parallel. Labels used are substances known per se to the person skilled in the art, in particular chemiluminescent compounds (for a general survey see, for example, Michelson, A. D. and Barnard, M. R., U.S. Pat. No. 5,552,290) (incorporated herein by reference).
The abovementioned flow cytometry is an established procedure, but has the disadvantage that it can be used only for the specific purpose of cell counting and/or typing. Usually, it is therefore also only established in specific laboratories. Wider use of the differentiation of cells and their activation states would be desirable, however, for clinical problems. For routine use, application in customary clinicochemical analyzers or other automated equipment is necessary for the routine laboratory.
The invention was therefore based on the object of making available an alternative to the previously customary flow cytometry methods, which allows the determination of cell surface antigens in a homogeneous, immunochemical procedure.
A number of homogeneous, immunochemical procedures for the determination of antigens and antibodies are already known, such as, for example, the FRAT1 System (Syva), the EMIT1 System, enzyme channeling immunoassays, fluorescence energy transfer immunoassays (FETI, e.g. TRACE1 Technology; CIS bio International), enzyme inhibitor immunoassays (Hoffmann LaRoche, Abbott Laboratories) or fluorescence polarization immunoassays (Dandlicker). These homogeneous procedures were developed in order to offer methods which can be carried out without separation and/or washing steps. Some of these procedures have only a limited sensitivity or are not suitable for the determination of high molecular weight analytes having multiple epitopes.
The expression scintillation proximity assay (SPA) was introduced by Hiram E. Hart and Elaine B. Greenwald (Molecular Immunology 1979; 16: 265-267) (incorporated herein by reference) in order to describe a specific homogeneous radioimmunoassay. In this procedure, two different types of polymeric beads are employed, which are loaded with specific binding components. The first of these bead types is additionally loaded with a dye while the second bead type additionally carries tritium. The dye has the property of emitting light pulses as soon as it is stimulated by the 1H xcex2-radiation (Auger electrons). This radiation, however, only has a range of a few micrometers in aqueous solutions, so that in dilute suspensions which contain both bead types, only a few beads of the one type are found in sufficiently close to beads of the other type. As a result, all in all only a small fluorescence signal can result. By means of the addition of reactants which can react with the specific binding components of the two bead types, however, an aggregation of the beads takes place which brings many of the beads of the first type (tritium beads) into the vicinity of beads of the second type (fluorophore beads), so that an altogether higher signal results. The resulting signal is detected in a scintillation counter. A further development of this procedure by use of 125iodine-labeled specific binding components was described by Udenfriend, S. et al. (Proc. Natl. Acad. Sci. 1985; 82: 8672-8676) (incorporated herein by reference).
A further procedure is described (EP-0 515 194 A2; Ullman et al., Proc. Natl. Acad. Sci. 1994; 91: 5426-5430 (incorporated herein by reference); Ullman et al., Clinical Chemistry 1996; 42: 1518-1526) (incorporated herein by reference) as a luminescent oxygen channeling immunoassay (LOCI). In this, two particle types are used, one of which contains a photosensitizer (sensitizer beads) and the other a chemiluminescent component (acceptor beads). The photosensitizer generates singlet oxygen and activates the chemiluminescent component if it is sufficiently close. The activated chemiluminescent component generates light which can be detected as a measuring signal.
Bystrak, S. et al. (Analytical Biochemistry 1995; 225: 127-134) (incorporated herein by reference) describe a homogeneous procedure in which a photooxidation of a fluorescent substrate, which is bonded to a unilaminar vesicle, by singlet oxygen takes place. Specific binding components are covalently bound to the surface of the vesicle.
These procedures all comprise specific binding of particles to binding components. As a rule, the binding of these binding components is carried out via the coating of the particles with appropriate specific ligands, such as, for example, antigens or antibodies for immunochemical detection. Up to now, these procedures were only used for the detection of soluble (humoral) factors. On binding to these factors (for example proteins), transmitter and receiver particles are brought into a spatial vicinity which allows a transfer of the energy emitted by a transmitter to a receiver particle. Use for the detection of insoluble, solid phase-associated factors, such as, for example, cell surface antigens, has not previously been pointed out.
Surprisingly, it was found in the context of the present invention that transmitter and receiver particles can be bound to a solid phase-associated factor which is multiply solid phase-associated such that the spatial vicinity necessary for the energy transfer is achieved independently of the size of the solid phase or, in other words, that the greatest distance between transmitter particles and receiver particles at which energy transfer can still take place is not exceeded. The solid phase can be, for example, a cell and the solid phase-associated factor can be, for example, a cell surface antigen. Surprisingly, it was thus possible to show that the extension of homogeneous immunochemical detection procedures, which until now were limited exclusively to the detection of humoral factors, to the detection of cell surface markers is possible, so that their determination can also be carried out in equipment based on a principle other than that of flow cytometry.
The present invention therefore relates to a procedure for the detection or for the determination of a solid phase-associated factor F, which is multiply associated with the same solid phase, in a sample. According to the invention, the sample is brought into contact with a first stable complex, consisting of at least one ligand L, which has binding affinity for F, and a transmitter T, as well as a second stable complex, consisting of at least one ligand L, which has binding affinity for F, and a receiver R, such that complexes F-L-T and F-L-R are formed. The signal is determined which results when T and R are sufficiently close to one another.
The present invention additionally relates to a procedure for the simultaneous detection or for the simultaneous determination of at least one first solid phase-associated factor Fx and a second solid phase-associated factor Fy, where Fx and Fy are associated with the same solid phase, in a sample. According to the invention, the sample is brought into contact with at least one first stable complex, consisting of at least one ligand Lx which has binding affinity for Fx, and a transmitter T, and also a second stable complex, consisting of at least one ligand Ly which has binding affinity for Fy, and a receiver R, such that complexes Fx-Lx-T and Fy-Ly-R are formed. The signal is determined which results when T and R are sufficiently close to one another.
According to a preferred embodiment, the stable complexes L-T, L-R, Lx-T or Ly-R comprise in each case particles, L or Lx being immobilized together with T on a first particle and L or Ly being immobilized together with R on a second particle.
More preferably, the solid phase is a cell, for example an erythrocyte, leucocyte, granulocyte, lymphocyte, monocyte, thrombocyte, or a cell from another tissue or organ. According to the invention, however, the term cell can also mean a prokaryotic or eukaryotic exogenous cell, such as a bacterium or parasite, or alternatively a subcellular parasite, for example a virus.
Solid phase-associated factors are to be understood as meaning both factors which are integrated into the solid phase and those factors which are not integrated into the solid phase, but are associated with it on account of other interactions.
A possible sample material is, for example, body fluid, tissue extract or ex-vivo cultures. Body fluids here are preferably blood, synovial fluid, cerebrospinal fluid, ascites or urine, particularly preferably whole blood or platelet-rich plasma.
The present invention furthermore relates to a procedure in which F, Fx and/or Fy is an integral membrane protein, a membrane-associated protein, a glycostructure or a lipid. The integral membrane protein can in this case be, for example, an integrin, selectin, a protein from the MHC complex or another known protein according to the cluster designation. Membrane-associated proteins are not integrated into the membrane, but detectable on the surface via specific ligand/receptor interactions, such as, for example, fibrinogen on fibrinogen receptors, antibodies against membrane proteins, complement factors or lectins against carbohydrate structures on the membrane surface and/or membrane proteins or processed antigen in the MHC complex on antigen-presenting cells. The membrane-associated proteins are furthermore proteins which are detectable on the surface via electrostatic interactions, such as, for example, active enzymes of the clotting system or proteins from the annexins family. The lipids according to the invention are substances known to the person skilled in the art from the acylglycerols, phosphoglycerides, sphingolipids, waxes, terpenes, steroids and/or prostaglandins group. According to the invention, the composition of the phospholipids of the surface membrane, such as, for example, the proportion of phosphatidylserine or of phosphatidylethanolamine, is preferentially detected by binding affinitive ligands, such as proteins from the annexins family, or by binding affinitive proteins of the clotting system such as, for example, activated protein C or protein S.
The present invention additionally relates to procedures in which the ligand binds to F, Fx or Fy via a mediatory binding component.
The present invention furthermore relates to procedures in which L, Lx or Ly is bound to particles via a biotin-avidin bridge.
The present invention moreover relates to procedures in which L, Lx or Ly can be an antibody, antigen, lectin, coenzyme, apoprotein, ligand of a receptor, substrate analog or annexin.
According to a preferred embodiment of the present invention, an energy transfer takes place between the transmitter T and the receiver R. This can be effected, for example, by radioactive processes, or by excitation of photosensitive dyes and direct or indirect electron transfer caused thereby, for example by means of activated oxygen. According to a further embodiment of the present invention, the energy transfer in the receiver particle leads to a reaction, for example an emission of luminescence, preferentially chemiluminescence, or fluorescence, which is detectable and a measure of the spatial vicinity of transmitter and receiver particles.
According to the invention, it is also possible by the addition of the substances modulating energy transfer known to the person skilled in the art in the particular system, for example damping substances, such as, for example, dyes or antioxidants, to decrease the minimum distance necessary between transmitter and receiver particle and thus to improve the measurement/background signal ratio.
The procedure according to the invention can be used, for example, for the characterization of cell types, subgroups or activation states of cells, and the detection of surface markers or surface antigens, for example neoepitopes in the context of tumor formation on cells. It can also be used for the typing of tissues or the characterization of tissue compatibility. In particular, the present invention also relates to the identification of exogenous cells, generally pathogens, such as bacteria. The process according to the invention is very particularly suitable for the identification of chlamydia.
xe2x80x9cTransmitterxe2x80x9d and xe2x80x9creceiverxe2x80x9d in the context of the present invention are understood as meaning members of classes of biological or chemical substance which can interact with one another in spatial vicinity, e.g. in the form of energy donors and energy recipients, such as, for example, photosensitizers and chemiluminescers (EP-0 515 194; Ullman et al. (1996) Clinical Chemistry 42:1518-1526), photosensitizers and fluorophores (WO 95/06877; Bystrak et al. (1995) Anal. Biochem. 225:127-134), or radioactive iodine125 and fluorophores (S. Udenfriend et al. (1985) Proc. Natl. Acad. Sci. 82:8672-8676), or fluorophores and fluorophores (Mathis, G. (1993) Clin. Chem. 39:1953-1959) or fluorophores and fluorescence quenchers (U.S. Pat. No. 3,996,345) each of which is incorporated herein by reference. The energy transfer can in this case take place from one substance to another, whilst a cascade of various substances through which the energy transfer runs is also possible.
An interaction between transmitter and receiver is, in particular, an energy transfer xe2x80x94i.e. the direct transfer of energy between transmitter and receiver, for example by means of light or electron radiation, and also by means of reactive chemical molecules.
In addition, the idea of an interaction between transmitter and receiver is also understood as meaning enzyme cascades. In this case, the substances are enzymes, of which at least one yields the substrate for another.
Also included in this are processes in which the activity of a substance is inhibited or increased by one or more others, for example the inhibition of or increase in enzyme activity or the inhibition of, increase in or change (e.g. wavelength shift) in the light emitted by the affected substance.
An effective interaction between transmitter and receiver takes place when these are spatially adjacent, i.e., for example, within a distance range of a few xcexcm, in particular within a distance range of less than 600 nm, preferably less than 400 nm, very particularly preferably less than 200 nm.
In a preferred embodiment of the procedure according to the invention, the interaction between transmitter and receiver is effected as an energy transfer, e.g. by means of the following methods, the references to which are incorporated herein by reference:
short-lived molecules, e.g. singlet oxygen (see also EP 0 515 194; Ullman et al. (1994) Proc. Natl. Acad. Sci. 91:5426-5430; Ullman et al. (1996) Clinical Chemistry 42:1518-1526, WO 95/06877 and Bystrak et al. (1995) Anal. Biochem. 225: 127-134),
radiation of low range, e.g. radioactive xcex2-radiation (see Hart and Greenwald (1979) Molecular Immunology 16:265-267 and Udenfriend et al. (1985) Proc. Natl. Acad. Sci. 82:8672-8676),
and/or energy transfer according to Fxc3x6rster (Mathis, G. (1993) Clin. Chem. 39:1953-1959; U.S. Pat. No. 5,527,684).
Included by the procedure according to the invention are also embodiments in which the surface of the particles has been further modified after their preparation and/or the particles are covered by one or more covalently or adsorptively bound layers or shells, for example of proteins, carbohydrates, lipophilic substances, biopolymers, organic polymers or mixtures thereof, in order, for example, to achieve improvements with respect to suspension stability, storage stability, shaping stability or resistance to UV light, microbes or other agents having a destructive action. The modifications and coverings can likewise be used here to reduce or to suppress the nonspecific binding to surfaces of reaction vessels and to those of protein constituents such as, in particular, proteins (e.g. albumin or antibody) or cell constituents (for example phospholipids or nucleic acids). Furthermore, the modifications and coverings are used to increase or to lower the hydrophobicity of the particle surface or the loading of the surface of the particles.
A further embodiment of the process according to the invention comprises employing, as transmitters or receivers, photosensitizers, for example acetone, benzophenone, 9-thioxanthone, eosin, 9,10-dibromoanthracene, chlorophyll, Buckminsterfullerene, Methylene Blue, Rose Bengal, porphyrins, phthalocyanines and/or their derivatives, and as chemiluminescent compounds, for example, olefins, 9-alkylidenexanthans, 9-alkylidene-N-alkylacridans, enol ethers, enamines, aryl vinyl ethers, dioxenes, arylimidazoles and/or lucigenin and it being possible for the singlet oxygen generated by the photosensitizer to activate the chemiluminescent compounds to emit light. Also preferred in the process according to the invention is the use of substances such as, for example, luminol and oxalate esters which react with singlet oxygen to give intermediates which can react with reagents known to the person skilled in the art with radiation of light.
As a rule, the chemiluminescent compounds emit light in the wavelength ranges over 300 nm. The fluorescence of plasma falls rapidly in the range from 500 nm and can be neglected above 550 nm. If higher wavelengths are required, the chemiluminescent compounds according to the invention can also be brought into contact with fluorophores which can be excited by the activated chemiluminescent compounds and emit at higher wavelengths. Suitable fluorophores are, for example, rhodamine, ethidium bromide, 5-dimethylaminonaphthalene-1-sulfonyl, europium chelates with the agent 3-(2-thienoyl)-1,1,1-trifluoroacetone [Eu(TTA)3 (TTA=3-(2-thienoyl)-1,1,1-trifluoroacetone)] or ruthenium chelates with the agent 2,2xe2x80x2-dipyridyl [Ru(bpy)3++(bpy=2,2xe2x80x2-dipyridyl)].
A further embodiment of the procedure according to the invention comprises employing photosensitizers and fluorescent compounds as substances and it being possible for the fluorescent compound for light emission to activate or, in a quench process, to suppress the light emission of the singlet oxygen generated by the photosensitizer. In particular, procedures according to the invention are preferred which comprise the use of fluorescent compounds which are subject to photooxidationxe2x80x94photobleachingxe2x80x94by reaction with singlet oxygen, such as, for example, 1,3-diphenylisobenzofuran, or react with singlet oxygen as photoactive precursors to give fluorophores, such as, for example, oxene umbelliferyl ethers or umbelliferyl selenides.
With respect to further examples of particles, photosensitizers, chemiluminescent or fluorescent compounds suitable for the procedure according to the invention, reference is made, in particular, to EP 0 515 194, Ullman et al. (Proc. Natl. Acad. Sci. 91:5426-5430, 1994) and Ullman et al. (Clinical Chemistry 42:1518-1526, 1996, WO 95/06877) each of which are specifically incorporated by reference.